Hello,
Maybe Johannes has more to add to this, but generally I feel that these kind of discussions get better feedback on the dtn-interest mailing list. I am not 100% sure we implement the DTN priorities 100% according to the spec, however we already discussed about the specified BP QoS/Prioritization internally and agree that this part of the specification is not very polished, i.e. maybe it should have just been left out of the spec altogether. Definitely we think, there is still room for reasonable QoS concepts for BP DTNS to be developed. For the time being, as far as I know, nobody in our group is actively pursuing this, so maybe this is your chance :)
MfG
Sebastian
Am 11.03.2013 um 13:38 schrieb Alex López lopalex87@gmail.com:
Hello all,
I've been studying how the priority parameter works with IBRDTN in a MANET that I have with 4 openwrt routers. My lab setup is the following:
Source 1 --\ \ \ Node 3 -------> End 4 / / Source 2---/
I've observed that if I try to send a file with a high priority from source 1 to End 4, and a file with low priority from source 2 to End 4, the file with low priority is received in End 4 before the file with high priority.
Reading the RFC 4838, it says the following:
Applications specify their requested priority class and data lifetime (see below) for each ADU they send. This information, coupled with policy applied at DTN nodes that select how messages are forwarded and which routing algorithms are in use, affects the overall likelihood and timeliness of ADU delivery.
The priority class of a bundle is only required to relate to other bundles from the same source. This means that a high priority bundle from one source may not be delivered faster (or with some other superior quality of service) than a medium priority bundle from a different source. It does mean that a high priority bundle from one source will be handled preferentially to a lower priority bundle sent from the same source.
Depending on a particular DTN node’s forwarding/scheduling policy, priority may or may not be enforced across different sources. That is, in some DTN nodes, expedited bundles might always be sent prior to any bulk bundles, irrespective of source. Many variations are possible.
If I understand well, the priority marking that is done in the Sources, it's lost in the intermediate Node 3, right? I cannot imagine why DTN works like this? It is really an stupid QoS no? Whats the reason behind this implementation? There is any way that the Node 3 recognizes the priority of the bundles that it has in custody? And from what source they are from?
Maybe it is because DTN is aiming for a only bidirectional communication between only 1 source and 1 end and multiple nodes? So a MANET could not be the best option to set a DTN implementation?
Thanks in advance.
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